1. Field of the Invention
The present invention relates to a wire electrode feeder for a wirecut electrical discharge machine.
2. Description of the Related Art
FIG. 23 illustrates the arrangement of a conventional wire electrode feeder disclosed in, for example, Japanese Patent Publication No. 31333 of 1988, wherein a workpiece 1 has a starting hole 2 pre-drilled at a machining start point. A wire electrode 11 is continuously provided to the work piece by a supply motor 3, via a supply pulley 4 coupled with the supply motor 3, and a clamp pulley 5 disposed opposite to the supply pulley 4. A first link 6 is extended to the clamp pulley 5, and a second link 7 is coupled to the end of the first link 6, the second link being pivotally moveable about support pin 8. A coil spring 9 is disposed between the second link 7 and an external fixture. A solenoid 10 is coupled with the end of the second link 7 which is opposite to the side thereof which is coupled to the coil spring 9. The wire electrode 11 is supplied through a wire electrode guide pipe 12, having a die-shaped upper wire electrode guide 13 made of diamonds. A sintered metal portion 14 is disposed on the lower end of guide pipe 12 for holding the upper wire electrode guide 13 to the lower end of the guide pipe 12. There also is a die-shaped lower wire electrode guide 15 that is made of diamonds and is held by a sintered metal portion 16 and set in a lower guide body 17. A pair of take-up rollers 18a and 18b are disposed opposite to each other with the wire electrode 11 therebetween, and a take-up motor 19 is coupled with the take-up roller 18b.
The operation of the wire electrode feeder shown in FIG. 23 will now be described. The workpiece 1 is placed on a work table (not shown) that is freely movable within a horizontal plane according to control commands. At the beginning of machining, the workpiece 1 is first set so that the starting hole 2, pre-drilled therein, is coaxial with the guide pipe 12. The clamp pulley 5 is then released by the restoring force of the coil spring 9. In this state, the wire electrode 11 is inserted from the top into the groove of the wire supply pulley 4. The solenoid 10 is then activated to press the clamp pulley 5 against the wire supply pulley 4 and the wire supply motor 3 is driven to feed the wire electrode 11 through the guide pipe 12 in the direction of the upper wire electrode guide 13. Since the upper wire electrode guide 13 and lower wire electrode guide 15 are supported to be coaxial with each other by a holding mechanism (not shown) at the beginning of machining, the wire electrode 11 passes through the upper wire electrode guide 13 and the lower wire electrode guide 15 and is inserted between the pair of take-up rollers 18a and 18b. In this state, the take-up rollers 18a, 18b and take-up motor 19 are ready to feed the wire electrode 11, and the clamp pulley 5 is released by energizing solenoid 10. The guide pipe 12 is then raised and removed from within the workpiece 1 by a moving mechanism (not shown), and the wire electrode 11 is thus inserted, under tension, in the workpiece 1.
To facilitate the above-described operation, the leading edge of the wire electrode 11 is reshaped by cut-off reshaping means (not shown) into a tapered shape so as to easily penetrate into the die-shaped upper and lower wire electrode guides 13, 15.
FIG. 24 illustrates an alternative conventional wire electrode feeder employing a supersonic vibrator used as a wire feed driving source to feed a wire electrode.
In this conventional device, first, a wire electrode 11 is inserted into the wire electrode guide 101 and a starting hole (not shown) provided beforehand in a workpiece 1. Subsequently, a presser plate 109 is released from a supersonic vibrator 106 by a releasing mechanism (not shown). The wire electrode 11 is led to a gap between the presser plate 109 and the supersonic vibrator 106, and the presser plate 109 releasing mechanism is reset to force the wire electrode 11 to be pressed against the supersonic vibrator 106 by the preload spring 108.
On completion of the wire electrode 11 stretching operation as described above, two free ends of the elastic body 104, are caused to each resonate in a flexure oscillating secondary mode and a vertical oscillation primary mode due to piezo-electric devices 105a, 105b. By causing the two modes to be 90.degree. out of phase, both ends of the elastic body 104 are made to vibrate, on elliptical locuses in an identical direction of rotation, friction-driving the wire electrode 11 in a predetermined direction. The elastic body 104 included in the supersonic vibrator 106 is designed so that the two vibration modes have an identical resonant frequency and so that the vibration frequency is equal to the resonant frequency so as to cause a standing wave.
Also, in the conventional wire electrode feeder arranged as described above, the wire must be fed between the wire supply pulley 4 and clamp pulley 5 by the wire supply motor until it passes through the workpiece and reaches the take-up rollers, or supersonic vibrator. Accordingly, the wire electrode may tend to curl due to a slight speed and/or mounting position difference between the two pulleys. Also, the wire may buckle midway in the feeding path from the supply pulley to the electrode guide before the wire electrode passes the electrode guide.
Further, in the second conventional device wherein the wire electrode driving source comprises the supersonic vibrator, the wire electrode cannot be fed through the workpiece automatically, and after the wire electrode has been fed therethrough, friction, which tends to prevent the wire electrode from being driven is generated between the presser plate and wire electrode which are continuously pressed against the vibrator, and further since the vibrator and presser plate are of a flat shape, the wire electrode may be deformed or forced out of position.